Mountune replacement air box that has the additional intake hose on the bottom of the filter housing. I recently put the stock Ford paper filter back in. Just not a fan of K&N style oil gaze filters. The oil gaze filters keep out bugs and small pebbles, but let pretty much everything else in. No magic here, shine a light and you can see open pin holes everywhere. Absolutely no felt difference with the paper filter in with my Mountune MP 215 tune. If it is loosing any horsepower it is not apparent at all. I am guess maybe 2 to 3 HP loss max, if that and probably only at max rpm's. When I look at how much more filter area there is with the stock paper filter (both number of pleats and depth of pleats), there is just so much more surface area than the K&N flat panel filters so I can't see flow is really much less as long as you keep a clean filter in.